Various types of hydraulic tools such as wrenches or pliers which may be held in one hand are known. The vast majority of these, however, require both hands of an operator to effect tool engagement or disengagement with the workpiece.
U.S. Pat. No. 3,058,214 of the present inventor shows a one-hand hydraulic tool comprising a frame and a stationary jaw fixed thereto; a movable jaw pivotally mounted in the frame for movement towards and away from the stationary jaw and including a cam member; a hydraulic power system disposed in the frame and including a liquid tank, a piston reciprocable in a cylinder and adapted to be pressed unconnectedly against the cam member of the movable jaw, thereby to impart a moment to the movable jaw, a pump connected to the tank by a suction duct and to the cylinder by a delivery duct, check valves in the suction and delivery ducts, a return duct from the cylinder to the tank, and a pressure release valve in the frame member for the operation of the tool; springy means acting on the movable jaw in opposition to the moment imparted to the movable jaw by the pressure exerted on the cam member by the hydraulic piston; and non-hydraulic means for mechanically imparting to the movable jaw a moment co-directional with the moment imparted to the movable jaw by the piston.
There is described and illustrated hereinbelow and claimed in copending U.S. Pat. App. Ser. No. 815,377 a further improvement and refinement of the apparatus described in the aforesaid U.S. patent and provides apparatus having enhanced ease of disengagement. There is thus provided in accordance with an embodiment of the invention a single-hand operated tool comprising:
first and second relatively movable elements adapted to be associated with a head assembly for application of pressure to a workpiece; PA0 a housing; PA0 a hydraulic pump disposed within said housing; PA0 hydraulic fluid communication means associated with said pump for exerting hydraulic force on said relatively movable elements; PA0 articulated lever means associated with said pump and arranged such that reciprocal motion of said lever means provided by the action of a single hand, unassisted, operates said pump and produces a desired force on said workpiece; PA0 release valve means for releasing the force exerted by said hydraulic fluid in response to a manual actuation produced by said single hand and including a valve stem and seat wherein the force urging seating of the valve stem against the valve seat is smaller than said desired force.
Additionally in accordance with an embodiment of the invention there is provided interchangeable hand held tool apparatus as described above wherein the first and second relatively movable members are coaxially disposed for engagement with an interchangeable head assembly and operation thereof.
The tools described above operate at a single speed and while they are provided with overpressure and overextension limiting means, they do not include automatic release apparatus operative at a selectable pressure threshold as would be particularly useful in crimping for producing uniform crimps.
Hydraulic jacks and pumps which operate at two speeds are well known. Examples are illustrated in U.S. Pats. Nos. 2,250,551 and 2,820,415. Shifting from one speed to another is accomplished in response to exceedance of a pressure threshold. This pressure threshold is established by a spring-loaded pressure sensitive valve which is operative to short circuit one of two pumping conduits when high pressures are encountered. It is to be emphasized that the known hydraulic jacks and pumps are relatively large tools operating at high fluid volume and relatively low pressure and are not designed to be small or to be operable by one hand of an operator.
In order to scale down the weight and physical size of hydraulic tools for the purpose of rendering them hand held and operable by one hand unassisted, the operating pressure thereof must be increased significantly. Otherwise the resultant force produced thereby would be scaled down proportionately with the tool size, greatly decreasing the tool's usefulness.
Conventional hydraulic tools operate at pressures up to about 10,000 p.s.i., that is, about 700 Atmospheres. Increasing the operating pressure above these limits involves difficulties arising out of the greatly increased forces exerted on the operating components of the tool, such as valves, valve stems and springs. Also, at such high pressures, the compressability of hydraulic fluid becomes a significant factor. These difficulties can be appreciated from a consideration of hydraulic devices known from the prior art. If one calculates the forces that result from multiplication of an operating pressure exceeding 700 Atm. by the exposed surface area of the parts concerned, one will find forces in the order of hundreds of kilograms, even if one designs the parts to be as small as possible.
Therefore, large forces require large springs and large valve stems to accommodate them. The large size of the springs and valve stems requires enlargement of the parts associated therewith and as a result the forces are further increased. It may thus be appreciated that a "vicious circle" is involved in the conventional design of high pressure tools in scaled down dimensions.
It is also to be appreciated that conventional hydraulic tools are not designed to be held and operated by one hand. Such tools therefore do not involve difficulties connected with the displacement of small amounts of hydraulic fluid. In the compression of very small amounts of hydraulic fluid, the compressability of the fluid becomes significant because when high pressures are reached the fluid is readily compressed to an extent that insufficient fluid remains to perform the required work.
It may thus be understood that scaling down of conventional hydraulic tools involves not only the problem of too-large forces but also the problem of fluid compressibility. No solutions to these problems have been proposed in the prior art.